Rongge

Presettable times for train stops in stations are indispensable if you want to operate your model railway more or less realistically according to a timetable. This circuit shows how a 555 timer can be used with a relatively small timing capacitor to generate very long delay times as necessary by using a little trick (scarcely known among model railway electronic technicians): pulsed charging of the timing net-work. Such long delays can be used in hidden yards with through tracks, for instance.  As the timer is designed for half-wave operation, it requires only a single lead to the transformer and one to the switching track or reed contact when used with a Märklin AC system (H0 or H1). The other lead can be connected to any desired grounding point for the common ground of the track and lighting circuits. Circuit diagram : Long-Delay Stop Switch Circuit Diagram As seen from the outside, the timer acts as a monostable flip-flop. The output (pin 3) is low in the quiescent state. If a ...

This timer circuit is designed to switch on a 12 V load in a solar-powered installation for a preset period at the press of a button. When the period has expired a latching relay disconnects both the load and the controller circuit from the 12 V supply. The length of the period can be configured by making suitable changes to the microcontroller’s source code. When button S1 is pressed a voltage appears across relay coil L1, and the relay switches the load on. Since the relay is a latching type, it remains in this state when the but ton is released. There is now a supply to the 78L05 voltage regulator (a low-dropout type such as the LP2950CZ-5.0 may also be used) and the microcontroller is powered up. In the microcontroller the timer program runs until the configured time interval has elapsed. Around 90 % of the way through the time period LED D2 lights as a warning that the load will shortly be switched off, and this time can also of course be configured by changing the software. When ...

This circuit shows how to build a super-sensitive, mini-powered FM transmitter consisting of a RF (radio Frequency) oscillator section interfaced with a high sensitivity, wide pass-band audio amplifier and capacitance mike with a built-in FET (Field Effect Transistor) that modulates the base of the RF oscillator transistor. Transistor Q1 forms a relatively stable RF oscillator whose frequency and is determined by the value of coil L1 and turning capacitor C4. Part List : R1_______15K R2_______3K9 R3_______220R R4,R5____1K R6,R9____10K R7_______390K C1,C6____0.01uF C2_______4.7pF C3_______0.1uF C4_______6-35pf trimmer cap C5_______2.2uF B1_______3V L1_______Coil winding (see below) Q1,Q2____PN2222 M1_______Special FET bypassed microphone Assemble L1 : Form L1 by tightly wrapping eight turns of #16 bus wire on a #8 wood screw. Produces an eight-turn coil with an inner diameter of approximately 0.135 inches and lenght of about 0.625 inches. Insert in the proper hole and solder as shown.